delete pics to save space

1.2742.cpp

@@ -0,0 +1,52 @@
+#include<cstdio>
+#include<cmath>
+#include<algorithm>
+using namespace std;
+struct Point
+{
+	double x,y;
+	Point(double _x=0,double _y=0):x(_x),y(_y) { }
+	inline bool operator<(const Point &b) { return x<b.x||(x==b.x&&y<b.y); }
+};
+typedef Point Vector;
+inline Vector operator+(const Vector &a,const Vector &b) { return Vector(a.x+b.x,a.y+b.y); }
+inline Vector operator-(const Vector &a,const Vector &b) { return Vector(a.x-b.x,a.y-b.y); }
+inline double Dot(const Vector &a,const Vector &b) { return a.x*b.x+a.y*b.y; }
+inline double Cross(const Vector &a,const Vector &b) { return a.x*b.y-a.y*b.x; }
+inline double Length(const Vector &a) { return sqrt(Dot(a,a)); }
+const double eps=1e-6;
+inline int dcmp(double x) { return fabs(x)<eps?0:(x>0?1:-1); }
+
+const int maxn=10005;
+int n; Point p[maxn],res[maxn];
+int ConvexHull(Point *p,int n,Point *res)
+{
+	sort(p,p+n);
+	int cnt=0;
+	for(int i=0;i<n;i++)
+	{
+		while(cnt>=2&&dcmp(Cross(res[cnt-1]-res[cnt-2],p[i]-res[cnt-1]))<=0) cnt--;
+		res[cnt++]=p[i];
+	}
+	int k=cnt;
+	for(int i=n-2;i>=0;i--)
+	{
+		while(cnt>k&&dcmp(Cross(res[cnt-1]-res[cnt-2],p[i]-res[cnt-1]))<=0) cnt--;
+		res[cnt++]=p[i];
+	}
+	if(n>1) cnt--;
+	return cnt;
+}
+int main()
+{
+#ifdef local
+	freopen("pro.in","r",stdin);
+#endif
+	scanf("%d",&n);
+	for(int i=0;i<n;i++) scanf("%lf%lf",&p[i].x,&p[i].y);
+	int size=ConvexHull(p,n,res);
+	double ans=0;
+	for(int i=0;i<size;i++) ans+=Length(res[i]-res[(i+1)%n]);
+	printf("%.2lf\n",ans);
+	return 0;
+}